This Part Fits the following kits / parts:

#88033 - PINION GEAR 33 TOOTH (0.6M)

E10/Not compatible with 48 and 64 pitch spur gears

Optional tuning gear for the E10. A lower tooth count on the
pinion gear will give you more acceleration, while a higher tooth
count will give you extra top speed. Have a selection of pinion
gears available so you can tune the speed of your car as
desired!